When you get tickets to Discovery Cove, they also include tickets to Sea World and Aquatica for 14 days anytime surrounding your DC reservation. You can also upgrade to the ultimate package for $25 which adds Busch Gardens for the 14 days, and also includes free parking at SW, Aquatica, and BG - if you are driving and going more than one day to one of these parks, getting at least one ultimate package will save money on parking alone.
I went in Feb with the ultimate package - did DC, 2 days SW, 1 day Aquatica, 1 day BG. Saved $80 on parking via the $25 ultimate package add on - you can't beat that. Plus BG was absolutely awesome with excellent rides and something for everyone to do. An easy day trip to drive to (or, they have a free bus if you don't have a car).
Depending on your dates, you might find DC deals through
undercover tourist - sadly I never did find any discounts on my date. Either way, book DC earlier than later as the prices increase as the date approaches.
You cannot secure a dolphin swim time until you arrive that day - they assign times as people check in.
Bring a good camera to get photos of the 3 doing the dolphin swim from the beach / surrounding rocks. If you ask, they'll point you to the best spot to get pictures (it will depend on which area your family is assigned).
Hit the aviary first thing when it opens, as the birds are much more enthusiastic and interactive then. There are 3 rooms to the aviary, and most people dawdle at the first one so if you walk through, you'll have a whole aviary room more or less to yourself for several minutes.